'\" et
.TH UNGETC "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
ungetc
\(em push byte back into input stream
.SH SYNOPSIS
.LP
.nf
#include <stdio.h>
.P
int ungetc(int \fIc\fP, FILE *\fIstream\fP);
.fi
.SH DESCRIPTION
The functionality described on this reference page is aligned with the
ISO\ C standard. Any conflict between the requirements described here and the
ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
.P
The
\fIungetc\fR()
function shall push the byte specified by
.IR c
(converted to an
.BR "unsigned char" )
back onto the input stream pointed to by
.IR stream .
The pushed-back bytes shall be returned by subsequent reads on that
stream in the reverse order of their pushing. A successful intervening
call (with the stream pointed to by
.IR stream )
to a file-positioning function (\c
\fIfseek\fR(),
\c
\fIfseeko\fR(),
\fIfsetpos\fR(),
or
\fIrewind\fR())
or
\fIfflush\fR()
shall discard any pushed-back bytes for the stream. The external
storage corresponding to the stream shall be unchanged.
.P
One byte of push-back shall be provided. If
\fIungetc\fR()
is called too many times on the same stream without an intervening read
or file-positioning operation on that stream, the operation may fail.
.P
If the value of
.IR c
equals that of the macro EOF, the operation shall fail and the input
stream shall be left unchanged.
.P
A successful call to
\fIungetc\fR()
shall clear the end-of-file indicator for the stream. The value of the
file-position indicator for the stream after all pushed-back bytes have
been read, or discarded by calling
\fIfseek\fR(),
\fIfseeko\fR(),
\fIfsetpos\fR(),
or
\fIrewind\fR()
(but not
\fIfflush\fR()),
shall be the same as it was before the bytes were pushed back. The
file-position indicator is decremented by each successful call to
\fIungetc\fR();
if its value was 0 before a call, its value is unspecified after the call.
.SH "RETURN VALUE"
Upon successful completion,
\fIungetc\fR()
shall return the byte pushed back after conversion. Otherwise, it
shall return EOF.
.SH ERRORS
No errors are defined.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.5" ", " "Standard I/O Streams",
.IR "\fIfseek\fR\^(\|)",
.IR "\fIgetc\fR\^(\|)",
.IR "\fIfsetpos\fR\^(\|)",
.IR "\fIread\fR\^(\|)",
.IR "\fIrewind\fR\^(\|)",
.IR "\fIsetbuf\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<stdio.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
